#include <stdio.h>
#include <stdlib.h>
#include <linux/rtc.h>
#include <sys/ioctl.h>
#include <sys/time.h>
#include <sys/types.h>
#include <fcntl.h>
#include <unistd.h>
#include <errno.h>
#include <time.h>

#define RTC_DEVICE 		"/dev/rtc"


int main(int argc, char *argv[])
{
    int fd, retval;
    struct rtc_time rtc_tm;
    time_t timep;
    struct tm *p;

    fd = open(RTC_DEVICE, O_RDONLY);
    if (fd == -1) {
        fprintf(stderr, "open /dev/rtc error\n");
        exit(errno);
    }

    /* Read the RTC time/date */
    retval = ioctl(fd, RTC_RD_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        exit(errno);
    }

    fprintf(stderr, "RTC date/time: %d/%d/%d %02d:%02d:%02d\n",
        rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900,
        rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

    time(&timep);
    p = gmtime(&timep);
    fprintf(stderr, "OS date/time(UTC): %d/%d/%d %02d:%02d:%02d\n",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);

    p = localtime(&timep);
    fprintf(stderr, "OS date/time(Local): %d/%d/%d %02d:%02d:%02d\n",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);
    
    rtc_tm.tm_mday = 15;
    rtc_tm.tm_mon = 11;
    rtc_tm.tm_hour = 15;
    rtc_tm.tm_min = 15;
    retval = ioctl(fd, RTC_SET_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        exit(errno);
    }
    
    /* Write the RTC time/date */
    retval = ioctl(fd, RTC_RD_TIME, &rtc_tm);
    if (retval == -1) {
        perror("ioctl");
        exit(errno);
    }
    fprintf(stderr, "RTC date/time: %d/%d/%d %02d:%02d:%02d\n",
        rtc_tm.tm_mday, rtc_tm.tm_mon + 1, rtc_tm.tm_year + 1900,
        rtc_tm.tm_hour, rtc_tm.tm_min, rtc_tm.tm_sec);

    time(&timep);
    p = gmtime(&timep);
    fprintf(stderr, "OS date/time(UTC): %d/%d/%d %02d:%02d:%02d\n",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);

    p = localtime(&timep);
    fprintf(stderr, "OS date/time(Local): %d/%d/%d %02d:%02d:%02d\n",
        p->tm_mday, p->tm_mon + 1, p->tm_year + 1900,
        p->tm_hour, p->tm_min, p->tm_sec);
    
    close(fd);
    return 0;
}